1. Field Of The Invention
The present invention relates generally to heat exchanging devices, radiators, and the like, and more specifically to an air-to-air heat exchanger for installing concentrically in line in a furnace flue.
2. Description Of The Related Art
It has long been recognized that heating a space by means of radiant heat (e. g., fireplace) is relatively inefficient, as most of the heat is lost through the chimney. While improvements have been made over the years, such heating systems, particularly where built into a wall where only a single opening in the wall provides heat for the entire room or space, are still relatively inefficient in comparison to modern central heating systems which heat the air itself and circulate the warm air through the structure by means of forced air or convective flow.
Nevertheless, such systems are still open to improvement, in that much of the heat developed in the system is lost through the furnace flue with the furnace exhaust gases. This is true with oil, natural or other gas, or other types of air circulation type heating systems.
Others have recognized this problem in the past, but solutions developed to this point have generally been directed to the recovery of additional heat from fireplace and chimney systems, rather than from air circulation heating or furnace systems. Those which have been developed for such heated air circulation systems, have not proven to be particularly efficient in terms of heat recovery from the furnace flue.
Accordingly, a need will be seen for a furnace flue heat exchanger or heat recovery system which is capable of recovering a large percentage of the heat of the furnace exhaust gases as they travel through the flue. The heat exchanger includes a plurality of relatively smaller pipes or tubes therein, axially parallel to the flue pipe in which they are installed. Furnace exhaust gases travel through the smaller pipes, with ambient air being forced through the remainder of the flue and about the outer surfaces of the smaller pipes, to be heated by the relatively hotter pipes carrying the flue gases.
The present device may be installed concentrically, in line in an existing furnace flue, either singly or plurally, and in either vertical, horizontal, or other orientation. A blower fan is provided, which may be actuated with the furnace blower motor, or by separate thermostatic means, as desired.
A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is provided below.
U.S. Pat. No. 2,355,495 issued on Aug. 8, 1944 to Edward M. Zier, Jr., titled "Heating And Air Conditioning System," describes a central heating system with which a below ground air reservoir is provided. Air is drawn from the below ground reservoir to be circulated about the furnace in winter. As the air from the below ground reservoir is warmer than ambient exterior air, less energy is required to heat the air from the below ground reservoir to the desired temperature. The air of the reservoir is relatively cooler than outdoor ambient in the summer, and is used for cooling during that season. However, Zier, Jr. does not disclose a heat exchanger which is installed concentrically in series with an existing flue pipe, as provided by the present invention.
U.S. Pat. No. 4,158,439 issued on Jun. 19, 1979 to John W. Gibbs, titled "Chimney Waste Heat Collector Requiring No Building Renovation," describes a system in which a series of units are stacked within a vertical chimney, and form a closed loop. Liquid is circulated through the units, to capture heat rising upwardly through the chimney. The system differs from the present heat exchanger, in that (1) the present system is not a closed loop system; (2) the present system is an air-to-air exchanger, and does not use a liquid; (3) the present system installs in-line in an existing furnace exhaust flue, rather than being installed within the existing flue pipe or chimney; and (4) the present system uses a series of axially parallel pipes within a larger flue pipe, with the smaller pipes serving as passages for the exhaust gas.
U.S. Pat. No. 4,160,524 issued on Jul. 10, 1979 to Clifford W. Stiber, titled "Circulating Fireplace With Adjustable Controls For Selectively Heating One Or More Rooms," describes a system having a passage concentrically formed about the firebox and chimney of a fireplace, to absorb heat therefrom. Air flows through the passage surrounding the chimney and firebox, and is selectively forced through ductwork to warm the room or rooms of the structure. (No fan is disclosed, but some means of forcing the air through the passageways would be required.) No heat exchanger installed in series with an existing flue pipe is disclosed by Stiber, as provided by the present invention. Also, Stiber does not provide an exhaust gas passage comprising a series of axially parallel pipes or tubes through a section of the flue or chimney, about which air is warmed for heating the structure, as provided by the present invention.
U.S. Pat. No. 4,455,994 issued on Jun. 26, 1984 to Matthew W. Homolik, titled "Woodburning Heating Stove And Heat Extractor," describes an air to air heat exchanger built into the back and upper portions of a woodburning stove. Various embodiments are disclosed, some of which include a plurality of either vertical or horizontal pipes within the heat exchanging unit. However, in each of these embodiments, the stove gases pass around the outside of the pipes, with air being heated by passing through the pipes, which arrangement is exactly opposite the present construction. Moreover, the Homolik system cannot be installed into an existing furnace flue, as provided by the present invention.
U.S. Pat. No. 4,469,276 issued on Sep. 4, 1984 to Al Marcum, titled "Heat Recovery Apparatus," describes a system somewhat like that of the Gibbs '439 U.S. patent described further above. Marcum provides one or more tubes extending vertically up a chimney, and a separate flue for exhausting combustion gases from the fireplace. Air is circulated up the tubes and passes downwardly between the tubes and the flue within the chimney, whereupon it is circulated into the room. The Marcum system cannot be installed in series with an existing furnace flue, as provided by the present invention, nor does Marcum provide a series of parallel exhaust gas passages within a larger passage, with air being heated by circulating about the series of exhaust gas passages, as provided by the present invention.
U.S. Pat. No. 4,699,315 issued on Oct. 13, 1987 to E. R. White, titled "Apparatus For Recovering Chimney Heat," describes a system somewhat similar to that of the Zier, Jr. '495 U.S. patent discussed further above. White provides inlet and return lines disposed exteriorly of the structure, which connect to a chimney cap. The working fluid circulating through these lines, receives heat from the fireplace gases rising from the chimney. The heated fluid is deposited in an underground storage tank for temperature maintenance and later recovery as desired, or passed directly to a forced air heating system to warm the air passing therethrough. The White system cannot be incorporated within the combustion gas flue of a forced air furnace or the like, as provided by the present invention.
U.S. Pat. No. 5,385,299 issued on Jan. 31, 1995 to Michael E. Zawada, titled "Fresh Air Intake System For A Dwelling Having Central Forced Warm Air Heating, " describes a system drawing exterior air into the cold air return duct of the heating system. The cold air is passed about a section of the furnace exhaust heater pipe, to be warmed before being drawn into the return duct. Zawada relies upon the main blower motor of the furnace to draw the air through his system, and uses it only to provide some fresh air into the interior of the structure. The Zawada pre-heater unit relies upon a heat muff surrounding the flue pipe, somewhat like a heater unit for air cooled automobile or aircraft engines, rather than circulating the air about a series of exhaust pipes passing through a larger flue pipe, as in the present invention.
Finally, U.S. Pat. No. 5,423,374 issued on Jun. 13, 1995 to Henry J. Miller et al., titled "Heat Exchanger For Flue Gas," describes a device which is installed in line with the flue of a stove, furnace or the like. However, Miller et al. require a larger diameter section of flue pipe, which must be assembled with reducers to the flue sections immediately preceding and following their heat exchanger. Moreover, Miller et al. use only two relatively large pipes within their larger diameter flue pipe. This is because they use the internal pipes for the circulation of room air, with the larger diameter flue pipe containing the flue gases which are routed about the exteriors of the internal pipes. Miller et al. do not provide any forced air means, thus requiring relatively large diameter pipes, unlike the present invention. In the present invention, flow is opposite that of the Miller et al. device, in that flue gases pass through the internal pipes within the flue, while air within the structure or room is passed about the exterior of the plurality of internal pipes, within the larger diameter pipe. While the present invention could rely upon air flow from the main blower fan, preferably a small fan having a capacity about equal to the furnace exhaust flow, is provided. This has been found to optimize the efficiency of the heat exchange operation in the present invention.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.